Elution process for the regeneration of spent activated carbon

ABSTRACT

Improvement in the process for the regeneration of spent activated carbon combining an aqueous alkaline solution and an organic solvent, such as a lower alcohol. The spent carbon is first contacted in a column under practically static conditions, and at between 25* and 90*C for 30 minutes to 2 hours with an aqueous alkaline solution, preferably 0.5 to 25 percent by weight sodium hydroxide. An alkaline treatment prepares the elution action of the solvent. The solvent is a lower alcohol, preferably isopropanol combined with water. The solvent is then removed by steam and the carbon is regenerated by an acid treatment. Complete regeneration is obtained.

limited States Patent 1 Renzaria et al.

[ 1 ELIJTION PROCESS FOR THE REGENERATION OF SPENT ACTIVATED CARBON [75]Inventors: Jacques Raphael Benzaria,

Chambly; Claude Zundel, Neuilly S/Seine, both of France [73] Assignee:Societe Anonyme: Degremont Societe Generale dEpuration etdAssainissement, Saint-Cloud Rueil Malmaison, France [22] Filed: June19, 1970 [2]] Appl. No.: 47,599

[30] Foreign Application Priority Data June 20, 1969 France ..6920827[52] US. Cl. ..252/413, 210/30, 210/40, 252/412, 252/414, 252/415 [51]Int. Cl; ..B01j 11/02 [58] Field of Search ..252/412, 413, 414, 420;127/55; 210/30, 39, 40

[56] References Cited UNITED STATES PATENTS 2,236,679 4/1941 Ferguson eta1 ..252/413 3,053,774 9/1962 Walther ..252/414 2,769,751 11/1956 Paull.....252/414 3,274,104 9/1966 Hamilton... .....252/412 3,053,774 9/1962Walther ..252/414 l lMalcl'l 13, 1973 FOREIGN PATENTS OR APPLICATIONS636,752 5/1950 Great Britain ..252/414 OTHER PUBLICATIONS PittsburghChemical C0. Technical Booklet Basic Design Techniques for ActivatedCarbon Adsorption Systems Published 1961 (Pat. Off. 9/23/63) pp. 1 & 4.

Primary Examiner-Daniel E. Wyman Assistant Examiner-P. E. KonopkaAtt0rneyLittlepage, Quaintance, Wray & Aisenberg [57] ABSTRACTImprovement in the process for the regeneration of spent activatedcarbon combining an aqueous alkaline solution and an organic solvent,such as a lower alcohol.

The spent carbon is first contacted in a column under practically staticconditions, and at between 25 and 90C for 30 minutes to 2 hours with anaqueous alkaline solution, preferably 0.5 to 25 percent by weight sodiumhydroxide. An alkaline treatment prepares the elution action of thesolvent. The solvent is a lower a1- cohol, preferably isopropanolcombined with water. The solvent is then removed by steam and the carbonis regenerated by an acid treatment. Complete regeneration is obtained.

17 Claims, N0 Drawings ELUTION PROCESS FOR THE REGENERATION F SPENTACTIVATED CARBON Regenerated activated carbons have been used for thepurification of sugar liquids, drinking water, various secondaryproducts of the foodstuffs industry, industrial waste water from themanufacture of dye stuffs, detergents, phenol derivatives, such as alkylphenols or nitrophenols.

The object of the invention is an improved process for the regenerationof spent vegetable or mineral activated carbon.

The use of vegetable or mineral carbon in powdered or granular form iswell known for the purification of solutions which are placed incontinuous or discontinuous contact with the said activated orunactivated carbons; these carbonshave the property of retaining certainof the products existing in the solutions treated; the amounts ofproducts retained by these carbons are very variable, from 1 to 30percent by weight of the purifying carbon, for instance.

The activated carbons used are generally adapted to adsorb the majorityof the organic materials in solution.

This adsorption depends on the polarity of the carbon, its structure,its basic nature and various characteristic values, such as the iodinevalue, methylene blue value, erythrosin value, molasses number,permanganate number determining, notably, the surface and thedistribution of pores in a carbon.

Each type of carbon should be adapted as a function of the polaritiesand sizes of the molecules to be retained. Carbon adsorption andsaturation are closely connected with the concentrations of reagents inthe solution to be treated, as well as the method used.

For reasons of economy, it quickly became apparent, mainly because ofthe high price of these so called activated carbons, that it wasnecessary to be able to regenerate them, as the known installations,operating on a lost carbon system, give excellent results from the pointof view of purification, but are difi'icult to operate economically.Many methods of regeneration have been tried, such as acid treatmentswith organic or inorganic acids, treatments with alkaline solutions(sodium, ammonia, hydroxide, etc.), with solvents and even gases(nitrogen, helium) and, most frequently, with mixed mixtures, or evenwith oxidizing chemical solutions.

U.K. Pat. No. 636,752, French Pat. No. 1,409,050 and U.S. Pat. No.2,763,580 can be cited as documents illustrating the prior art in thefield of the regeneration of certain adsorbent materials.

UK. Pat. No. 636,752 relates specifically to the reactivation of spentadsorbent inorganic materials such as clay, silica gel, bauxite (oralumina), It provides a treatment for spent material combining a firstwater miscible liquid polar solvent and a second nonpolar solventimmiscible with the first. The organic impurities are extracted and thesolvent phases separated. In the preamble to U.l(. Pat. specificationNo. 636,752 it is indicated thatit has already been suggested thatalkaline substances mixed with solvents should be used as substances forthe regeneration of such adsorbent inorganic materials. Examples ofalkaline substances are aqueous and/or alcoholic alkali hydroxides orammonia. The neutral organic solvents used are selected from alcohols,ketones, aromatic and aliphatic hydrocarbons. It is also stated thattreatment with an alkali hydroxide dissolved in a solvent, such asalcohol, is very effective to remove acid impurities, but that thistreatment has the drawback of subsequently requiring an additionaloperation consisting in a treatment with strong acid. Although UK. Pat.No. 636,752 does not concern the problem of the regeneration ofactivated carbon, it can be cited as a document illustrating the priorart, to show that these lixivation techniques do not give entiresatisfaction.

French Pat. No. l,409,050 relates essentially to the preparation of aspecial adsorbent carbon, activated by a preliminary operationconsisting in contacting said carbon with an aqueous solution containinga lower alcohol and an aromatic hydrocarbon, such as benzene or toluene.This carbon is used to purify solutions containing amino acids, and toseparate the said acids. The acids adsorbed can be recovered by elutionwith an aqueous solution of a lower alcohol (10 to 50 percent by volume)and ammonium hydroxide (l to 5 percent by volume). Such a patent shouldbe considered as being limited to the preparation of an adsorbent carbonactivated in a special manner for the aforesaid application, that is tosay, to obtain certain amino acids.

U.S. Pat. No. 2,763,580 describes a process for the purification ofsugar liquids in which an aqueous solution of sugar is passed through abed of granular activated carbon. The saturated adsorbent carbon can beregenerated by washing with an alkali solution containing from 1 to 15percent solids, and notably a solution of sodium hydroxide or potassiumhydroxide.

A drawback common to all the known lixivation processes is that theynecessitate large amounts of treatment liquids, ranging, for instance,from 10 to times the volume of carbon treated. Furthermore, theactivated carbon rapidly loses its activity as it undergoes successiveregeneration steps. It is, therefore, necessary to regularly andcontinually replace by a new product a relatively large amount of activecarbon which gradually becomes saturated, as a result of which the costof treatments is uneconomic;furthermore, the organic materials are onlypartially extracted and the remaining ones decrease the activity of theadsorbent material when it is subsequently used.

In addition, when the products retained are organic, other knownprocesses consist in partially calcining the spent carbon attemperatures in the range of 500 to 970C in furnaces with a controlledatmosphere. A good regeneration requires very accurate conditions oftemperature and atmosphere and a minimum of 1 kg steam/kg carbon isnecessary to obtain good regeneration.

Operations of the furnace are difficult, they involve a large capitaloutlay and require careful supervision. Carbon regeneration is poor ifcalcination is carried out at too low a temperature in an uncontrolledatmosphere, and considerable losses occur due to burning. Regenerationat too high a temperature renders the carbon fragile, resulting in aloss of fines which cannot be disregarded. On the other hand, badfurnace control generates stake gases. As carbon regeneration proceeds,a certain amount of fines is produced which are drawn off in the fluegas. The average loss observed in industrial installations is recognizedas being in the range of 5 to 10 percent when furnaces are properlysupervised.

The average price of one ton of carbon regenerated on the spot,including absorption of depreciation, can attain 40 to 50 percent theprice of new carbon.

Another drawback of the treatment of spent carbon by calcination is thatregeneration is not total, and that when the carbon is used again itdoes not possess all the properties of new carbon; notably, theinorganic salts which may be adsorbed in the carbon are not removed bycalcination, which further decreases the adsorption capacity of thecarbon as successive operations of regeneration and re-use are carriedout The present invention does away with the drawbacks of the prior artprocesses described hereinabove. It makes use of elution technique in anew manner allowing for the nature of the adsorbent used which will betaken as a non-limiting example hereinafter.

The objects of the invention are a process for the regeneration of spentvegetable or mineral carbon by elution under economically moreadvantageous conditions owing to the small amounts of treatmentsolutions used with respect to the volume of carbon;

a process such that carbon regeneration is more complete than in knownprocesses a process which can be used both for granular carbon andpowdered carbon;

- a process entailing a very low capital outlay on materials.

Generally speaking, the invention consists in first changing thepolarities of activated carbon by means of an alkaline substance, suchas an alkali hydroxide, and then displacing the adsorbed substances by asolvent by a new method and under carefully controlled conditions, inremoving the solvent by the injection of steam or superheated water andrestoring the initial condition of carbon by acid washing.

The invention therefore relates to a process for the regeneration ofspent vegetable or mineral activated carbon by contacting it in a columnwith a combination of an alkaline substance and solvents, characterizedin that the alkaline treatment is carried out at a temperature at leastequal to the ordinary temperature, for a period of 30 minutes to 2 hoursunder practically static conditions of contact of the alkaline solutionand carbon, an aqueous solution containing at least one organic solventthen being circulated in the column at a different flow velocity, thesolvent is removed by injection of steam and the carbon is washed withan acid, after which it can be re-used.

The essential characteristic of the invention resides in the fact thatthe alkaline treatment is carried out statically, or under conditions ofpractically stationary flow of the alkaline solution in the column,whereas elution by the solvent is effected under different conditions ofvelocity. In this description, the expression practically staticconditions of contact," means that during contacting of the carbon andalkaline substance, the latter circulates in the column at a very slowflow velocity or at zero flow velocity. Thus, in batch treatment, flowvelocity is zero. In a continuous embodiment, the flow velocity of thealkaline substance is sufficiently slow for the conditions of theduration of contact to be respected. The velocity in all cases beingslower than 1 m/hour.

The elution solvent, on the other hand, circulates in the column at adifferent, higher velocity which can, for instance, reach a velocity ashigh as 10 m/h.

As an alkaline substance, sodium, potassium or ammonium hydroxide isused; an aqueous solution of sodium hydroxide is preferred. Alkalihydroxide concentrations of 0.5 to 25 percent by weight are suitable forthe aqueous solution.

The alkaline treatment temperature lies in the range of 20 to 130C,preferably in the range of 25 to 90C and advantageously in the range ofto 80C.

For the solvent treatment step, there is used an aqueous solution of atleast one organic solvent preferably selected from lower alcohols andother polar solvents such as acetone and dichloroethane. As a loweralcohol there is used, notably, methanol, ethanol, propanol, isopropanolor butanol. The preferred alcohol for carrying out the process isisopropyl alcohol, owing to its high power of adsorption by carbon, andthe ease with which it is recovered. A hydroalcoholic solutioncontaining 20 to percent by volume of isopropyl alcohol can be usedadvantageously.

The temperature of the solvent treatment depends on the nature of thelatter solvent. This temperature is generally preferably lower than ornear to the boiling temperature of the solvent, or of its solution, atthe pressure in the reaction zone. In the case of high temperatures, itis advantageous to carry out regeneration at the vapor pressure of thetreatment solution.

The essential characteristic of the invention is that the pre-treatmentwith the alkaline solution is such that it prepares for elution with thesolvent subsequently used, so that the said solvent will completelyreplace the organic materials and that, consequently, the carbonregeneration will also be effected with maximum efficiency.

It has, moreover, been ascertained that the use of a singlehydroalcoholic alkali solution could be suitable in as far as thepreliminary pretreatment passage is carried out at a very slow flowvelocity. The treatment can then be considered as static in the sense ofthe present invention, where in the case of a hydroalcoholic sodiumhydroxide solution, only the sodium hydroxide is active, the alcohol andwater only being carriers. When this step is terminated, the flowvelocity can be accelerated by 5 to 10 times and complete elution isthen obtained as when the operation is carried out with separatehydroxide sodium and alcohol solutions.

Additionally, as the materials initially retained by adsorption in thecarbon are retained in a certain volume of eluant solvent, it ispossible to envisage the recovery of organic substances in the measurethat they are of economic importance. In this connection, the use ofisopropyl alcohol as the elution solvent is advantageous, as thisalcohol can be easily and almost completely recovered by thedistillation of its azeotrope; finally, the operation is economicalowing to the small amounts of elution substance used.

After drying, the treatment of the invention comprises, an injection ofsteam enabling the solvent, which has taken the place of the productsadsorbed by the carbon during use, to be extracted from the carbon. Thetemperature and pressure of the steam should be adapted to each case;these values can easily be determined by those skilled in the art.

Steam at two bars, optionally superheated, can be used for carrying outthe invention. As a variant, it is possible to use hot water under highcompression, which is circulated in the column, or even a stream of hotair.

Following this treatment, and in order to reactivate the carbon, thelatter is treated withan acid to remove the inorganic derivatives whichit has adsorbed, such as sulphur derivatives, carbonates, metal salts,etc. The acid is preferably an inorganic acid such as hydrochloric acid,sulphuric acid or phosphoric acid. It can also be an organic acid suchas formic acid or acetic acid.

The final operation can be completed by rinsing in clean water.

The process of the invention can be carried into effect equally wellwith granular carbon and powdered carbon. Only the equipment used forcarrying out the process is different. In the case of granular carbon,the treatment is carried out on a bed of grains which may be as deep asmeters.Powdered carbon, on the other hand, is treated in systems whichenable it to be retained in thicknesses not exceeding 30 to 40 cm. Theflow velocities are then reduced, but the results are similar. It shouldbe noted that the carbons used in the process of the invention, whetherthey be powdered or granular, have a surface area per unit mass ofbetween about 500 to 1500 mlg.

The process of the invention is applicable in all cases wherereactivation of spent vegetable or mineral activated carbon isnecessary. Some fields of application of the invention are, among othersthe reactivation of activated carbons which have been used for thepurification of sugar liquors;.these carbons, which can contain up topercent of their weight of organic substances, including amino acids,are reactivated continuously, or in batch operation, in vertical columnshaving a diameter to height ratio of 1 10, using either separatedsolutions of sodium-hydroxide and alcohol, or by the mixed solution withmodification of the flow velocity during pretreatment and duringelution, this velocity changing, for instance, from 1 to 5.

- the regeneration of activated carbons which have been used for thepurification of drinking water.

- the regeneration of activated carbons which have been used for thepurification of industrial waste water from factories manufacturing dyesor phenol derivatives, alkyl phenols, detergents or nitrophenols.

- the regeneration of activated carbons which have been used for thepurification of domestic or industrial waste water, either for aphysicochemical treatment or for a tertiary treatment.

The process according to the invention is also suitable for treatingglycerine and sorbitol manufacturing liquors, the first obtained fromthe soap industry, the second initially obtained from potato starch. Theinvention provides finally a simple and economical process for theregeneration of activated carbons used in certain foodstuff industries.7

In order to put the process of the invention into practice, the spentactivated carbon can be extracted for subsequent reactivation andreplaced by a new charge.

Two columns can also be operated alternately, one being used for thepurification of a liquid containing impurities while the other is eithertreated and regenerated in situ, or emptied and recharged with newcarbon.

Finally, continuous extraction of saturated activated carbon can beeffected, and it can be replaced, also continuously, by a new product;many technically perfected installations have been in operation forseveral years, either using continuous, uninterrupted extraction, or bybatch extraction of a portion of the saturated activated carbon,replacing it by an equivalent amount of new or regenerated carbon.

It should also be noted that the process of the invention can also beapplied to the regeneration of adsorbent products other than activatedcarbon, such as molecular sieves, and ion exchange resins among others.

The invention will now be illustrated by the following examples:

EXAMPLE 1 The object of this example is to show the critical aspect ofthe conditions of flow of treatment solutions in a column of spent,activated carbon as they are provided for in the invention.

A certain amount of carbon is available, this has been used for thepurification of waste water from a chemical factory producing organicdyes; this carbon is of a uniform brownish color.

This carbon is loaded into a glass tube having a diameter equal to onetenth of its length (d=3cm, l 30cm); the column of spent carbon issuitably packed to prevent preferential passages; the tube is positionedin a double glass casing through which hot water is run to raise thecarbon to a temperature of between 50 and C.

The top of the column is connected to a metering pump which permits thesupply of variable and measurable amounts of solutions; the bottom ofthe column being connected to a glass tube onto which there is secured aphotoelectric cell which is connected to a graphic recorder; the flow ofcolorless liquid through this tube is represented by a zero linearrecording; when, on the other hand, a colored liquid flows through thistube, the recorder registers this flow by measuring the opacity thereof,which is a function of the amount of coloring matter in the circulatingliquid, this measurement is qualitative and becomes quantitative if themagnitude of the surfaces defined is determined by the lines registeredon the graph (the time being given in abscissa and the relative opacityin ordinates).

A. Various liquids are flowed through this column, which if filled andequipped in the manner described, and the results obtained are noted onthe recorder. The following facts were observed a. nothing is recordedif pure water is flowed through the column b. a slight, continuouscoloration is registered on the recorder is an aqueous solution ofsodium hydroxide containing 1 to 5 percent NaOl-I is flowed through thecolumn;

c. the same observation as in (b) is made with acidulated water, whichis inorganic with sulphuric acid or organic with acetic or formic acid.

It is established that, whatever the liquid used, it must be used inamounts of 10 to times the volume of carbon in order to obtain acolorless transit liquid,

and the carbon treated is seen to gradually become uniformly black, butin no case does it regain the initial color of new carbon; it cantherefore be said that regeneration is only partial, whatever the methodof treatment used,whatever the flow velocity of liquids and thetemperatures thereof, and whatever the total amount of liquid flowingthrough said column.

B. The process of the invention is used as a comparison, this trialconsists in placing a sodium hydroxide solution containing 40 g ofsodium hydroxide per liter, viz normal sodium hydroxide (N), in staticcontact with the carbon column, in maintaining the temperature of thecolumn at 80C for a period of 1 hour, and then injecting ahydroalcoholic solution containing 50 percent isopropyl alcohol into thetop of the column. Photoelectric measurement, backed up by pHmeasurements and titrimetry, show that when a volume of aqueous sodiumhydroxide substantially equal to the volume of carbon flows through thecolumn it is only slightly opaque, and therefore only has a low dyecontent but a very high pH, and that the liquid suddenly becomes opaquewhile the pH of the solution tends to become neutral. Titrimetry showsthat practically all the sodium hydroxide passes during the period ofslight opacity, and it is also seen that the opaque solution contains noalcohol; as the alcohol is injected, the liquor becomes paler and thealcohol content increases until the alcohol solution runs clear, andafter the passage of 2 equivalent volumes of the hydroalcoholicsolution, it is seen that the carbon has regained its normal color andthat the impurities have been completely washed out of it;it is,therefore, then ready to be treated with steam and then with acid inorder to be reused. It was, however, observed that whereas discolorationis continuous and homogenous during the passage of a simple sodiumhydroxide solution, it occurs in this case by a downward movement of thecoloration zone, as if a colored annular zone descended through thecarbon column in a homogenous manner and in one step.

Without limiting the invention to a theoretical interpretation of thephenomena involved, it is thought that:

l. the treatment by the sodium hydroxide containing solution hasprepared the removal of materials retained on the carbon, probably owingto a change in polarity 2. the treatment by the alcohol solution hasrepulsed" these impurities, and the alcohol replaces these impurities inthe pores of the carbon; the alcohol seems to act as an eluant ratherthan as a solubilizer.

EXAMPLE 2 The aim of this example is to show the synergy of the stagesof treatment of the process of the invention.

In the same apparatus as in example 1, carbons which have been used forthe decolorization of sugar liquors are treated under the followingconditions a. a treatment is carried out with aqueous sodium hydroxidealone; after circulation, the solution is found to contain only 0.49percent extracted material;

b. a treatment is carried out with aqueous isopropyl alcohol alone thesolution is found to contain only 1.4 percent extracted material;

c. the treatment is carried out according to the invention as in example1 (part B) and the solution is found to contain 2.38 percent extractedmaterial.

A comparison and calculation of the volumes and extracted materials inthe three preceding cases (a), (b) and (c) shows that the total amountextracted in case (c) was 140 percent with respect to the treatment withsodium hydroxide alone (a) and l60 percent with respect to alcohol alone(b).

EXAMPLE 3 A solution containing 10 ppm chlorophenol and 5 ppm of variousdetergents is flowed through a bed of granular inorganic carbon having asurface area in m/ grams of approximately 1,000. When the solutionemerges, after this treatment, at a concentration of 10 percent of thestarting solution, the carbon is considered as having lost itsefficiency. It is ready for regeneration.

After drying, the carbon is treated in a column having a height between5 and 10 diameters and provided with a double reheating casing.

A solution containing 7 g sodium hydroxide 105 g pure isopropyl alcohol128 cc H O is introduced into the column and left in contact with thecarbon in a stationary regime for 1 hour at C. This solution is thencirculated through the carbon at 80C at a rate of l m/h.

The liquid is then drained from the column. Steam is introduced and thesolvent recovered. Finally, a 5 percent solution of hydrochloric acid isintroduced after the steam.

The carbon obtained is regenerated and can be reused immediately.

EXAMPLE 4 A filtered water from the residues of a dye factory,containing various chemical products which are considered as beingimpossible to identify, is percolated through a column of granularcarbon. The carbon is saturated after 300 liters of the liquid haveflowed through the column. About 20 percent organic materials areretained on the carbon. The carbon is then treated as in example 3 givenhereinabove. It is then recycled as new carbon. The results obtainedwith the recycled carbon for adsorption and decolorization of sugarliquors are similar to those obtained with the initial carbon.

EXAMPLE 5 The spent carbon used in the preceding example is treated at50C with an ammonium solution containing, by weight, 10 percent ammonia,60 percent ethanol and 30 percent H,O. Carbon desorption is much longer,and the results show that the carbon has only recovered -90 percent ofits initial adsorbant properties.

EXAMPLE 6 Water from a factory producing nitrated derivatives, such asthat obtained from the manufacture of nitrobenzene or nitrotoluene, isflowed, after filtration,

on a column of granular, inorganic or vegetable carbon, having a surfaceunit area in the range of 1,000 to 1,200 m lgram.

The column is considered as being saturated when the solution flowingout of the column shows indications of the presence of organic residues.

After drying the column the following mixture is introduced into it:

- 5 percent sodium hydroxide 70 percent acetone 25 percent water.

The solution is introduced onto the carbon and the whole is left tostand for one hour. The product is then treated as in the precedingexamples.

The regenerated carbon is then directly reusable.

EXAMPLE 7 The same spent carbon is used as in the preceding example 6,and it is treated under the same conditions with a solution comprising(by weight) 5 percent sodium hydroxide 80 percent dichloroethane 15percent water Results equivalent to those of example 6 are obtained.

EXAMPLE 8 This example relates to a test treatment, by activated carbon,of nonconcentrated sugar liquors before evaporation.

In a column consisting of a vertical glass tube 130 cm in length and 10cm in diameter provided with a porous horizontal plate at the bottomthereof, there was flowed an aqueous slurry consisting of saturatedactivated carbon from a column used for treating sugar liquors; thewater which forms part of the slurry still charged with elements to betreated is flowed through the porous surface; the column so constitutedis checked to ensure its perfect homogeneity, without faults or holes.

After the saturated activated carbon has been dried in an oven at 100C,it was examined to confirm that, at equal volume of identical newcarbon, it showed a weight increase generally of between and 25 percent,the maximum corresponding to a saturation level such that the apparentdensity of the saturated activated carbon was 0.650.

The volume of the adsorbent column being approximately 10 liters, hotwater at 90C was first flowed through it to raise the temperature of thewhole to about 60 to 70C. As a comparative test, 100 liters of anaqueous sulphuric acid solution at 10 percent by weight of acidpreviously heated to 100C was flowed downwardly; the liquid at thecolumn outlet was seen to be colored (the color of strong tea), thecolumn was then washed with hot water; after having emptied the column,a portion of the carbon was dried, and after sampling the adsorbentcarbon it was seen that, based on an identical volume of new carbon, theweight remained substantially higher for a value between 105 and 115percent that of new carbon.

Another comparative trial was then carried out in the same manner, usinga sodium hydroxide solution at 10 percent by weight of sodium hydroxideand under the same conditions, it was seen that an equal volume of newcarbon and dried, treated carbon weighted between 103 and H0 percent, tothe disadvantage of the carbon treated with the sodium solution, theliquor at the outlet being as dark as concentrated coffee.

A trial was then carried out according to the invention, using anaqueous solution containing between 30 and 60 percent by weight ofisopropyl alcohol and 10 percent by weight of sodium hydroxide under thesame conditions as above, that is, at a temperature of 60 to 80C. Thissolution was left standing in contact with the spent carbon for 1 hour,the same solution was then flowed at a rate of 1.30 m/hour for 2 hours.

It was then found that the same volume of new active carbon and spentcarbon regenerated under these conditions were of substantially the sameweight, and that the iodine values were similar to those of new carbon.In this last trial, total extraction of the products retained during theclarification and purification treatment of sugar liquors was obtained.

We claim:

1. A process for regenerating spent vegetable or mineral activatedcarbon, comprising (a) subjecting said carbon to an alkaline treatmentby contacting said spent carbon in a column with an aqueous alkalinesolution having a flow velocity of zero to less than 1 m/hour throughsaid column at a temperature of about 20 to 130C., for a period of about30 minutes to 2 hours to change the polarity of the carbon and conditionit for solvent displacement of the adsorbed substances on said carbon,(b) eluting said adsorbed organic substances by solubilizing anddisplacing said adsorbed organic substances on said carbon with anaqueous organic solvent eluting solution, which is passed through saidcarbon in said column at a higher flow velocity than said alkalinesolvent, and wherein said organic solvent is selected from the groupconsisting of lower alcohols, acetone and dichloroethane, (c) removingsaid eluting solvent residue from the carbon by the injection of steaminto the said carbon, and (d) washing the carbon with acid to removeadsorbed inorganic material.

2. The process of claim 1 wherein said aqueous alkaline solution isselected from the group consisting of aqueous solutions of potassiumhydroxide, sodium hydroxide and ammonium hydroxide.

3. The process of claim 2 wherein said alkaline liquid is an aqueoussolution containing 0.5 to 25 percent by weight of sodium hydroxide.

4. The process of claim 1 wherein said alkaline treatment temperature isin the range of 25 to 90C.

5. The process of claim 1 wherein said alkaline treatment temperature isbetween and 80C.

6. The process of claim 1, wherein the elution solvent is selected fromthe group consisting of methanol, ethanol, propanol, isopropanol andbutanol.

7. The process of claim 6 wherein the elution solvent is an aqueoussolution containing 20 to percent by volume of isopropyl alcohol.

8. The process of claim 1 wherein said temperature of the treatment withthe elution solvent is lower than the boiling temperature of saidsolvent at the pressure in the reaction zone.

9. The process of claim )1 wherein said temperature of treatment withthe elution solvent is approximately that of the boiling temperature ofsaid solvent at the temperature in the reaction zone.

10. The process of claim 1 which is carried out continuously and whereinthe said alkaline treatment is carried out at a slow flow velocity ofsaid alkaline solution over the carbon, the said velocity not exceeding1 m/h.

11. The process of claim 1 wherein the circulation velocity of saidelution solvent is faster than 1 m/h and up to and including m/h.

12. The process of claim 1 wherein a aqueous alkaline hydroalcoholicsolution is used for the alkaline treatment step (a) and for the elutionstep, (b) in which case the circulation of the said solution during thealkaline treatment is carried out under practically stationary flowconditions, whereas the circulation of the said same solution during theelution step is effected at a different velocity above lm/h.

13. The process of claim 12 wherein the flow velocity of the saidaqueous alkaline hydroalkaline solution during the elution step is about5 times faster than during the alkaline treatment.

14. The process of claim 1 wherein said activated carbon has a surfacearea in the range of 500 to 1500 m /g.

15. The process of claim 1 wherein, instead of circulating steam overthe said activated carbon it is contacted with super heated water underpressure.

16. The process of claim 1 wherein hot air is injected onto the saidactivated carbon instead of steam.

17. The process of claim 1 wherein after the said steam said acid isselected from the group consisting of inorganic hydrochloric, sulphuricand phosphoric acids and the organic acetic and formic acids.

* l I t

1. A process for regenerating spent vegetable or mineral activatedcarbon, comprising (a) subjecting said carbon to an alkaline treatmentby contacting said spent carbon in a column with an aqueous alkalinesolution having a flow velocity of zero to less than 1 m/hour throughsaid column at a temperature of about 20* to 130*C., for a period ofabout 30 minutes to 2 hours to change the polarity of the carbon andcondition it for solvent displacement of the adsorbed substances on saidcarbon, (b) eluting said adsorbed organic substances by solubilizing anddisplacing said adsorbed organic substances on said carbon with anaqueous organic solvent eluting solution, which is passed through saidcarbon in said column at a higher flow velocity than said alkalinesolvent, and wherein said organic solvent is selected from the groupconsisting of lower alcohols, acetone and dichloroethane, (c) removingsaid eluting solvent residue from the carbon by the injection of steaminto the said carbon, and (d) washing the carbon with acid to removeadsorbed inorganic material.
 2. The process of claim 1 wherein saidaqueous alkaline solution is selected from the group consisting ofaqueous solutions of potassium hydroxide, sodium hydroxide and ammoniumhydroxide.
 3. The process of claim 2 wherein said alkaline liquid is anaqueous solution containing 0.5 to 25 percent by weight of sodiumhydroxide.
 4. The process of claim 1 wherein said alkaline treatmenttemperature is in the range of 25* to 90*C.
 5. The process of claim 1wherein said alkaline treatment temperature is between 70* and 80*C. 6.The process of claim 1, wherein the elution solvent is selected from thegroup consisting of methanol, ethanol, propanol, isopropanol andbutanol.
 7. The process of claim 6 wherein the elution solvent is anaqueous solution containing 20 to 75 percent by volume of isopropylalcohol.
 8. The process of claim 1 wherein said temperature of thetreatment with the elution solvent is lower than the boiling temperatureof said solvent at the pressure in the reaction zone.
 9. The process ofclaim 1 wherein said temperature of treatment with the elution solventis approximately that of the boiling temperature of said solvent at thetemperature in the reaction zone.
 10. The process of claim 1 which iscarried out continuously and wherein the said alkaline treatment iscarried out at a slow flow velocity of said alkaline solution over thecarbon, the said velocity not exceeding 1 m/h.
 11. The process of claim1 wherein the circulation velocity of said elution solvent is fasterthan 1 m/h and up to and including 10 m/h.
 12. The process of claim 1wherein a aqueous alkaline hydroalcoholic solution is used for thealkaline treatment step (a) and for the elution step, (b) in which casethe circulation of the said solution during the alkaline treatment iscarried out under practically stationary flow conditions, whereas thecirculation of the said same solution during the elution step iseffected at a different velocity above lm/h.
 13. The process of claim 12wherein the flow velocity of the said aqueous alkaline hydroalkalinesolution during the elution step is about 5 times faster than during thealkaline treatment.
 14. The process of claim 1 wherein said activatedcarbon has a surface area in the range of 500 to 1500 m2/g.
 15. Theprocess of claim 1 wherein, instead of circulating steam over the saidactivated carbon it is contacted with super heated water under pressure.16. The process of claim 1 wherein hot air is injected onto the saidactivated carbon instead of steam.